Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1493—Selection of liquid materials for use as absorbents

Definitions

• a second category is generally referred to as the aqueous base scrubbing process or "hot pot” process.
• a small level of an amine is included as an activator for the aqueous base used in the scrubbing solution.
• This type of process is generally used where bulk removal of an acid gas, such as CO 2 , is required. This process also applies to situations where the CO 2 and feed gas pressures are high. In such processes, useful results are achieved using aqueous potassium carbonate solutions and an amine activator.
• a third category is generally referred to as the nonaqueous solvent process.
• water is a minor constituent of the scrubbing solution and the amine is dissolved in the liquid phase containing the solvent.
• up to 50% of the amine is dissolved in the liquid phase.
• This type of process is utilized for specialized applications where the partial pressure of CO 2 is extremely high and/or where many acid gases are present, e.g., COS, CH 3 SH and CS 2 .
• U.S. Pat. No. 2,360,861 teaches the use of cyclic tetramethylene sulfones for separating mixtures of organic compounds and U.S. Pat. Nos. 2,385,704 and 3,475,329 teach the extraction of SO 2 with cyclotetramethylene sulfones.
• U.S. Pat. No. 2,176,441 to Ulrich et al teaches the use of amino acids having a primary, secondary or tertiary amino group and at least two nitrogen atoms to remove acidic gases.
• the patentees provide various general formulae for the amino acids taught to be useful in the acid gas scrubbing process. While certain "sterically hindered amines" can be derived by proper choice of substituent groups in the general formulae there is no teaching that these amines will achieve any unexpected results, such as improved regeneration rates coupled with high rates of absorption.
• a process for the substantial removal of acidic gases from a normally gaseous mixture which comprises contacting said normally gaseous mixture with an amine-solvent liquid absorbent comprising:
• an amine mixture comprised of at least 50 mol % of a sterically hindered amine and at least about 10 mol % of a tertiary amino alcohol, wherein said sterically hindered amine contains at least one secondary amino group which is part of a ring and is attached to either a secondary or tertiary carbon atom or a primary amino group attached to a tertiary carbon atom, and
• the liquid absorbent composition of the present invention may optionally contain up to about 35 weight % of water, preferably up to 25 weight % water and more preferably 10 to about 20 weight % water.
• the water in the liquid absorbent is used to generate steam (to help the heat balance of the overall process), reduce the viscosity of the solvent, particularly sulfolane and glycol type solvents) and assist the solubility of some amine-acid gas reaction products.
• solvent and "organic solvent” as used herein are meant to include those materials which appear to act in a purely physical manner, absorbing acidic gases physically without the formation of any apparent reaction product.
• solvent and organic solvent are to be contrasted with the so-called “chemical solvents” which involve the formatipon of salts or other decomposable reaction products with acidic gases.
• acidic gases is meant to include CO 2 , H 2 S, SO 2 , SO 3 , CS 2 , HCN, COS and the oxygen and sulfur derivatives of C 1 to C 4 hydrocarbons in various amounts as they frequently appear in gaseous mixtures.
• acidic gases which are generally CO 2 , H 2 S and COS may be present in trace amounts within a gaseous mixture or in major proportions, the major proportion preferably being CO 2 for the purpose of the present invention.
• the contacting of the amine-solvent liquid absorbent and the acidic gases may take place in any suitable contacting tower.
• the normally gaseous mixture from which the acidic gases are to be removed may be brought into intimate contact with the absorbing solution using conventional means, such as a tower packed with, for example, ceramic rings or saddles or with bubble cap plates or sieve plates, or a bubble reactor.
• the absorption step is conducted by feeding the normally gaseous mixture into the base of the tower while fresh and/or regenerated absorbing solution (i.e., the liquid absorbent of the present invention) is fed into the top.
• the normally gaseous mixture freed largely from acidic gases emerges from the top.
• the temperature of the absorbing solution during the absorption step is in the range from about 20° to about 100° C, and more preferably from 40° to about 60° C.
• the pressure of the normally gaseous mixture feed will preferably be in the range from about 1 to about 200 psig, and more preferably in the range from about 100 to about 1000 psig.
• the contacting takes place under conditions such that the acidic gases, e.g., CO 2 possibly in combination with H 2 S and/or COS are absorbed by the solution.
• the solution is maintaied in a single phase.
• the liquid absorbent composition comprising the amine mixture and solvent which is saturated or partially saturated with gases, such as CO 2 and H 2 S, may be regenerated so that it may be recycled back to the absorber.
• the regeneration should also take place in a single liquid phase.
• the regeneration or desorption is accomplished by conventional means, such as pressure reduction, which causes the acid gases to flash off or by passing the solution into a tower of similar construction to that used in the absorption step, at or near the top of the tower, and passing an inert gas such as air or nitrogen or preferably steam up the tower.
• the temperature of the solution during the regeneration step should be in the range from about 50° to about 170° C, and preferably 80° to 150° C.
• the absorbing solution after being cleansed of at least a portion of the acid bodies, may be recycled back to the absorbing tower. Makeup absorbent may be added as needed.
• an amine mixture comprising at least 50 mol %, preferably at least 65 mol %, of a sterically hindered amino alcohol and at least about 10 mol %, and preferably 20 to about 35 mol % of a tertiary amino alcohol, wherein said sterically hindered amino alcohol contains at least one secondary amino group which is part of a ring and is attached to either a secondary or tertiary carbon atom or a primary amino group attached to a tertiary carbon atom, wherein the total amine concentration in said liquid absorbent is in the range from about 10 weight % to about 65 weight %, preferably from 40 weight % to about 55 weight %, and
• an organic solvent which is a solvent for said amine mixture and a physical absorbent for said acidic gases, said contacting being conducted at conditions whereby the carbon dioxide containing acidic gases are absorbed, preferably at temperatures ranging from about 20° to about 100° C, and more preferably from 40° to about 60° C, and at a pressure ranging from about 1 to about 2000 psig, preferably 100 to about 1000 psig, and
• the regenerated liquid absorbent composition may thereafter be recycled to the absorber as is or it may be combined with fresh makeup scrubbing solution.
• the sterically hindered amines are preferably sterically hindered amino alcohols which include those amino alcohols which contain at least one secondary amino group which is part of a ring and is attached to either a secondary or tertiary carbon atom or a primary amino group attached to a tertiary carbon atom.
• the most preferred sterically hindered amino alcohols useful in the practice of the present invention include the 2-piperidine alkanols such as 2-piperidine methanol and 2-piperidine ethanol.
• amines that can be used include 2-(1-hydroxyethyl)-piperidine, 5-hydroxy-2-methyl piperidine, 2-methyl-3-hydroxy piperidine, 2,6-dimethyl-3-hydroxy piperidine and 2,5-dimethyl-4-hydroxy piperidine, 3-amino-3-methyl-1-butanol, 2-amino-2-methyl-1-butanol, 2-amino-2-methyl-3-butanol and 3-amino-3-methyl-2-pentanol.
• the solvents useful in the practice of the present invention are preferably organic compounds which will (1) contain at least one functional group to solubilize the amines; (2) be unreactive with the amines; (3) be a liquid at room temperature; (4) have a solubility for CO 2 at 25° C and one atmosphere of not less than about one volume of CO 2 per volume of solvent; and (5) have a boiling point at atmospheric pressure of at least about 150° C.
• Suitable sulfone derivatives include 2-sulfolene; 2-methyl tetramethylene sulfone; 3-methyl tetramethylene sulfone; 2,3-dimethyl tetramethylene sulfone; 2,4-dimethyl tetramethylene sulfone; 3,4-dimethyl cyclotetramethylene sulfone; 2,5-dimethyl cyclotetramethylene sulfone; 3-ethyl cyclotetramethylene sulfone; 2-methyl-5-propyl cyclotetramethylene sulfone as well as their analogues and homologues.
• sulfoxides useful as solvents in the practice of the present invention include the alkyl-, cycloalkyl- or arylsulfoxides, for example, those sulfoxides of the general formula:
• the following compounds are nonlimitative examples of the sulfoxides which are useful solvents: dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, dibutyl sulfoxide, methylethyl sulfoxide, dicyclohexyl sulfoxide, methylcyclohexyl sulfoxide, diphenyl sulfoxide, ethylphenyl sulfoxide, cyclohexylphenyl sulfoxide and tetramethylene sulfoxide.
• Dimethyl sulfoxide is the most preferred sulfoxide to be used as a solvent for the liquid absorbents of the invention.
• A is an alkylene radical which is either linear or branched, having from 2 to 15 carbon atoms and preferably 2-5 carbon atoms;
• R 11 and R 12 are the same or different, e.g., hydrogen atoms, hydrocarbon monovalent radicals having, for example, from 1 to 20 carbon atoms, for example, alkyl, cycloalkyl or aryl radicals;
• m is an integer of 1 to 20 and preferably 1 to 10.
• glycols are nonlimiting examples of the glycols, polyethylene glycols, polyalkylene glycols and their mono- and diethers useful as solvents for the liquid absorbents: glycol; diethylene glycol; heptaethylene glycol; decaethylene glycol; 1,3-propylene glycol; hepta(1,3-propylene glycol), tetra-(1,4-butylene glycol), polyethylene glycol of abut 400 molecular weight; and tri(1,3-propylene glycol).
• the preferred compounds of this class are the polyethylene glycols and their monoalkyl ethers.
• 1,3-dioxoheterocyclic compounds useful in the practice of the present invention can be represented by the following general formulae: ##STR2## wherein R 13 to R 18 represent hydrogen, lower alkyl groups containing 3 to 5 carbon atoms, lower alkyl groups substituted with OH, OR, or phenyl groups, or unsubstituted phenyl groups so selected that the molecular ratio of carbon atoms to oxygen atoms is between 1 and 10.
• aromatic hydrocarbons and aromatic ethers useful in the practice of the present invention include those compounds which are liquid at the absorption temperatures, for example, benzene, toluene, orthoxylene, metaxylene, ethylbenzene, paraethyl toluene, diphenyl ether, and their homologues having up to 12 carbon atoms.
• the pyrrolidones and piperidones useful in the practice of the present invention include the N-alkyl pyrrolidones and the N-alkyl piperidones having 4 to 12 carbon atoms, for example, 2-pyrrolidone, N-methyl pyrrolidone, N-ethyl pyrrolidone and N-methyl piperidone.
• the organic solvent component of the liquid absorbents of the present invention may include a mixture of two or more of the compounds described above.
• a typical composition useful for scrubbing a normally gaseous mixture having a high concentration of carbon dioxide and hydrogen sulfide will be comprised of about 50-60 weight % of the amine mixture, 1 to 15 weight % of at least one organic solvent, preferably sulfolane, and the balance water.
• solutions rich in carbon dioxide may be first scrubbed by a bulk scrubbing process using the "hot pot" process, preferably the processes disclosed in U.S. Ser. No. 590,427 and U.S. Ser. No. 750,520, filed Dec. 15, 1976, entitled “Process for Removing Acid Gases with Hindered Amines and Aminoacids,” the disclosures of which are incorporated herein by reference.
• This coarsely prepurified gas may then be treated in accordance with the teachings of the present invention to remove the last residues of the carbon dioxide containing gases.
• the solution is brought to 40° C, then the reactor is evacuated and CO 2 is admitted into it. 36 liters of CO 2 are absorbed.
• the rich solution so obtained is transferred to the desorber, where it is heated at 105° C for 15 minutes.
• the regenerated solution so obtained is transferred back to the absorber and subjected again to absorption. 31.9 liters of CO 2 are absorbed.
• a new solution is prepared, in which one-third of the piperidine ethanol is replaced by an approximately equivalent amount of a tertiary amine.
• the solution has the following composition:
• Example 2 Compared to the solution of Example 1, in this solution one-third of the piperidine ethanol has been replaced by an equivalent amount of a tertiary amino alcohol.
• the solution is subjected to the same cycle as before, i.e., absorption into fresh solution, desorption and absorption into lean solution.
• Table III gives the amounts of CO 2 absorbed into lean solution as a function of time. The total amount absorbed into the lean solution is 29.5 liters.
• Example 2 Compared to the solution in Example 1, in this solution one-third of the piperidine ethanol has been replaced by an approximately equivalent amount of a tertiary amino alcohol.
• the solution is subjected to the same cycle as before, i.e., absorption into fresh solution, desorption and absorption into lean solution.
• Table IV gives the amount of CO 2 absorbed as a function of time. The total amount absorbed into the lean solution is 29 liters.
• the process of the present invention in addition to providing the advantages of an improved lower heat of reaction and a lower cost amine mixture compared to the use of sterically hindered amines alone, also enjoys the advantage of improved "working capacity" compared to a process operating under substantially the same conditions without the use of a sterically hindered amine as disclosed and claimed in U.S. Ser. No. 590,427, filed June 26, 1975, the disclosure of which is incorporated herein by reference.
• the term "working capacity” relates to the thermodynamic cyclic capacity, that is the loading as measured at equilibrium conditions.
• This working capacity may be obtained from the relation between the CO 2 pressure in the gas and the CO 2 loading in the solution at equilibrium at a given temperature.
• the following parameters must usually be specified: (1) CO 2 absorption pressure, (2) CO 2 regeneration pressure, (3) temperature of absorption, (4) temperature of regeneration, (5) solution composition, that is weight percent amine, and (6) gas composition.
• the improved working capacity which results by the use of the sterically hindered amine and the tertiary amino alcohol in the solvent and optionally water can be determined by direct comparison with a process wherein a sterically hindered amine is not included in the amine-solvent scrubbing liquid.
• a carbon dioxide containing acidic gas is removed from a normally gaseous stream by means of a process which comprises, in sequential steps, (1) contacting the normally gaseous feed stream with an aminesolvent liquid absorbent at conditions whereby said carbon dioxide containing gas is absorbed in said liquid absorbent, and (2) regenerating said liquid absorbent at conditions whereby said acid gas is desorbed from said liquid absorbent, the improvement which comprises operating said process at conditions whereby the working capacity is greater than obtained under substantially the same conditions of absorption and desorption except that said liquid absorbent does not include a sterically hindered amine and a tertiary amino alcohol, wherein said working capacity is defined as the difference in moles between CO 2 loading in the liquid absorbent at absorption conditions (step 1) and the CO 2 loading in the liquid absorbent at regeneration conditions (step 2) when measured at equilibrium conditions.

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• 1977
  • 1977-02-14 US US05/768,420 patent/US4100257A/en not_active Expired - Lifetime
  • 1977-12-20 CA CA293,446A patent/CA1089842A/en not_active Expired
  • 1977-12-30 GB GB54258/77A patent/GB1593420A/en not_active Expired
• 1978
  • 1978-01-11 AU AU32343/78A patent/AU512737B2/en not_active Expired
  • 1978-01-11 IT IT19174/78A patent/IT1092728B/it active
  • 1978-01-25 NL NL7800908A patent/NL7800908A/xx not_active Application Discontinuation
  • 1978-02-02 DE DE19782804418 patent/DE2804418A1/de active Granted
  • 1978-02-13 BR BR7800854A patent/BR7800854A/pt unknown
  • 1978-02-13 JP JP1422178A patent/JPS53100180A/ja active Granted
  • 1978-02-13 FR FR7804032A patent/FR2380061A1/fr active Granted

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